Method and means for increasing the drag on falling missiles



April 23, 1963 J. J. TENNYSON 3,086,463

METHOD AND MEANS FOR INCREASING THE DRAG ON FALLING MISSILES Filed Dec. 2, 1959 Tlql.

JNVENTOR. 472mm J. Aha/W0 BY iinited States 3,086,463 METHOD AND MEANS FGR INCREASING THE DRAG 9N FALLING MTSSILES James E. Tennyson, 32 Brill Ava, Waterford, Qonn. Filed Dec. 2, 1959, Ser. No. 856,879 3 Qlairns. (Cl. 102-3) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to increasing the drag on missiles falling toward the earth at high speed. The term missile is used in a broad sense and relates to a nose cone portion of a missile, or to a r e-entering satellite, and to other man-made space traversing bodies that have a forward end and a trailing end when falling.

An object of this invention is to reduce damage due to aerodynamic friction on a missile moving at high speed through the atmosphere.

A further object is to minimize the disintegration of a missile on the return portion of its trajectory.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

FIG. 1 illustrates an embodiment of this invention on a missile, and

FIG. 2 illustrates a circuit arrangement for the magnetic field generating means.

This invention utilizes the fact that an electron can be driven off a body of solid material by supplying enough energy instantaneously to that electron to overcome the forces constraining the electron to remain within the material; Work function refers to the quantity of energy required by the electron to enable it to escape. The energy may be supplied thermionically, photoelectrically or in other forms. Substantial quantities of electrons can be driven or evaporated from a body in this manner. This effect is most commonly utilized in thermionic electron tubes; it is utilized in this invention.

Solid bodies traveling through the atmosphere at hypersonic speed leave an ionic trail. In Journal of Applied Physics, November 1957, Partridge and Harris report the measurement of electron density in the trails of high velocity pellets of between and 10 electrons per centimeter of path for velocity ranges of 1.0-4.5 kilometers per second and also report the relative velocities at which aluminum, magnesium, and magnesium-lithium alloy leave ionization trails. In the same edition of the Journal, Hendricks reports the measurement of electron density of between 10 and 10 electrons per centimeter of path length for pellet velocities ranging from 1.48 to 2.67 kilometers per second. These reports clearly indicate that an electron trail is left by high velocity missiles. Energy transferred to the outside surface of the missile as a result of aerodynamic friction produces electron evaporation and the electrons are left behind by the moving mis sile.

In its broader aspects this invention concerns generating a magnetic field locally at the trailing end of the missile transverse to the path thereof when falling toward the earth for interacting with the trail of electrons to affect a drag on the falling missile.

The missile 10 shown in FIG. 1 includes a pair of rigid struts l1 and 12 at its trailing end. A rigid magnetic field coil 13 is secured to the struts l1 and 12. The coil 13 consists of a high conductivity metal coated with a high work function material such as platinum to protect the coil from bombardment of the electron stream. The coil 13 may be a balanced Y arrangement as shown in FIG. 2. The coil is connected in circuit with a battery 14 and a normally open thermal switch 15 supported near the leading end of the missile; the switch is selected for closing when its temperature rises to a selected level anticipated during the fall of the missile through the atmosphere toward the earth. The battery may be any of the batteries providing a good ratio of power output to weight and size. The battery is required to provide power for only a very brief period. No resistance element is included in series with the battery since it may be operated at substantially short circuit during its duty period. The duty period of the battery need not be coincident with the entire interval of excessive temperature. lf eifective even for only a fraction of that interval any disintegration that might occur is reduced. The magnetic field need not be the only expedient relied upon for resisting disintegration. Disintegration is resisted by a heat sink design or by controlled ablation at the leading end. This invention contributes toward decreased disintegration. The broken lines 16 illustrate the paths of electrons that escape from the leading end of the missile and form a trail behind the falling missile.

The forward end of the missile, in the direction of fall, may include a surface layer of a material with a low thermionic work function, e.g., a magnesium alloy so that electron evaporation may take place at a temperature which is substantially lower than that at which the missile deteriorates.

Where the embodiment illustrated in FIG. 1 is a nose cone, the struts and coil are included within the propulsion stage until the latter drops ofi.

In operation, when the nose cone is on its return path toward the earth and approaches the more dense atmosphere, aerodynamic friction causes heating which is most pronounced at the leading end. Electron evaporation from the surface at the leading end becomes appreciable as the temperature rises.

The evaporated electrons will leave the coating material at velocities on the order of several kilometers per second and will come to rest after one or more violent collisions with molecules of oxygen and nitrogen of the atmosphere where the mean free path is on the order of one to ten centimeters at pressures of 10* to 10* of the pressure at the earths surface. This information is published in Radio Astronomy by Lovell and Clegg published by John Wiley and Sons. The magnetic field generated by coil 13 when the thermal switch 15 is actuated is drawn through the arrested electrons at the missile velocity.

When the leading end of the missile rises above the actuation temperature of switch 15, the switch closes and connects the battery to the magnetic coil arrangement 13 which in turn generates a magnetic field transverse to the direction of travel. The magnetic field moving with and just behind the missile is drawn through the evaporated and arrested electrons at the velocity of the falling missile. This results in a. drag on the falling nose cone.

As the magnetic field moves through the trail of electrons there is generated an electric field perpendicular to both the direction of electron flow and the direction of the magnetic field. This electric field in turn produces an electric current in the same direction as the electric field. The quantity of electric current is dependent upon the conductivity of the fluid. From information pro vided in The Physics of Fully Ionized Gases by Spitzen, page 84, equation 5-37, if the number of electrons per cubic centimeter is conservatively estimated to be 10 and the temperature is estimated to be -1000 K., the resultant conductivity is mh-os/meter. This current in turn reacting with the magnetic field, creates a mechanical force or induction drag which acts opposite to the direction in which the missile is moving, thus tending to reduce the speed of the missile. Assuming at a particular instant that the velocity is 5 kilometers per second and the magnetic induction is 0.5 Weber per square meter, the magnetic viscous force opposing the missile is as follows where F=force per unit volume.

Since one newton is equal to 0.25 pound in gravita tional units, the induction drag for the assumed condi tions is 62,000 pounds, which is significant even if applied for only a small fraction of the anticipated time interval during which the temperature level may tend to deteriorate the leading end of the missile. However, it is important to bear in mind that even less drag or slowing effect will tend to reduce deterioration even if applied for a brief period.

Alternate methods of construction may include making the field coils an integral part of the missile body using small coils but of greater length or providing magnetic coils and supporting struts that may be folded back while launching and in initial flight but released into position by a frangible element ruptured by an explosive charge following exhaustion of the propellant.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. A method of increasing the drag on a missile falling through the earths atmosphere toward the earth for the purpose of reducing the disintegrating effect of aerodynamic friction, where the missile is of the type that has a particular part that is at the trailing end during its fall, and where the missile leaves an ion trail during its fall, which comprises generating a local substantially constant magnetic field rearward of and exterior to the trailing end part of the missile and exposed to and intersecting any fluid medium in the wake of the missile during at least part of the time that the missile is falling and is leaving an ion trail and which said magnetic field moves with the trailing end of the missile, and is oriented generally nor- 4 m-al to the axis of the missile and interacting with the ion trail for exerting a drag on the falling missile.

2. A method of reducing the disintegration of the nose cone of a missile passing through the atmosphere at hypersonic speeds with resultant emission of a trailing stream of conducting fluid, which comprises creating a substantially constant continuous magnetic field in the wake of and normal to the direction of travel of the missile to intersect the trailing stream of conducting fluid to increase the drag on said missile.

3. The method of reducing the disintegration of a body while moving at hypersonic speeds in the atmosphere, which comprises providing on the exposed surface of said body, a layer of a material which emits a high density stream of electrons when its exposed surface is heated to temperatures created by such speeds, and creating a substantially constant continuous magnetic field in the wake of and normal to the direction of travel of the body to intersect the trailing stream to exert a drag on said body.

4. An improved missile capable of falling at hypersonic speeds through the atmosphere which comprises a body having on its nose an exposed surface of a material which emits a trailing stream of electrons when heated to temperatures created by said speeds, and means disposed rearward of and exterior to and carried by and moving with said body for creating in said trailing stream in the wake of said missile local to and external to said body a constant magnetic field oriented generally normal to the missile axis, for at least part of the time that the missile falls and that by interaction of said magnetic field with said trailing stream exerts a drag on the falling movement of said body.

References Cited in the file of this patent UNITED STATES PATENTS 2,431,319 Ellwood Nov. 25, 1947 2,555,384 Watt June 5, 1951 2,850,978 Franklin Sept. 9, 1958 2,882,824 Larsen Apr. 21, 1959 2,921,518 Huntoon Jan. 19, 1960 OTHER REFERENCES Physics, Part II (Halliday and Resnick), published by John Wiley & Sons Inc., '1960' (pages 689 and 690 relied on). (Copy in Div. 10.) 

1. A METHOD OF INCREASING THE DRAG ON A MISSILE FALLING THROUGH THE EARTH''S ATMOSPHERE TOWARD THE EARTH FOR THE PURPOSE OF REDUCING THE DISINTEGRATING EFFECT OF AERODYNAMIC FRICTION, WHERE THE MISSILE IS OF THE TYPE THAT HAS A PARTICULAR PART THAT IS AT THE TRAILING END DURING ITS FALL, AND WHERE THE MISSILE LEAVES AN ION TRAIL DURING ITS FALL, WHICH COMPRISES GENERATING A LOCAL SUBSTANTIALLY CONSTANT MAGNETIC FIELD REARWARD OF AND EXTERIOR TO THE TRAILING END PART OF THE MISSILE AND EXPOSED TO AND INTERSECTING ANY FLUID MEDIUM IN THE WAKE OF THE MISSILE DURING AT LEAST PART OF THE TIME THAT THE MISSILE IS FALLING AND IS LEAVING AN ION TRAIL AND WHICH SAID MAGNETIC FIELD MOVES WITH THE TRAILING END OF THE MISSILE, AND IS ORIENTED GENERALLY NORMAL TO THE AXIS OF THE MISSILE AND INTERACTING WITH THE ION TRAIL FOR EXERTING A DRAG ON THE FALLING MISSILE. 